Crankshaft machining device

ABSTRACT

A device for machining the crank pins of a crankshaft which are radially offset from the crankshaft axis of rotation. A first master shaft having an axis of rotation and radially offset crank pins corresponding to the crank pins of the crankshaft is rotatably mounted in a housing. A substantially identical master shaft is rotatably mounted to one end of a cradle which has its other end pivotally mounted about the axis of the first master shaft and movable between a first and second position. A girt is rotatably mounted to each of corresponding crank pins on both master shafts so that, as the master shafts are rotatably driven in synchronism with each other and with the crankshaft, cyclical movement is imparted to each girt. A broach is attached to each girt adjacent the crankshaft so that, as the cradle is moved from its first to its second pivotal position, the broach moves tangentially with respect to the crankshaft crank pins and thereby machines the crank pins.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to a device for machining the crank pinsof a crankshaft.

II. Description of the Prior Art

Crankshafts of the type used in internal combustion reciprocal pistonengines include at least two main bearings which are rotatably mountedto the engine crankcase and a plurality of crank pins to which thepiston connecting rods are rotatably attached. Furthermore, these crankpins have an axis substantially parallel to, but radially spaced from,the rotational axis of the crankshaft. Consequently, the crank pins movecyclically during rotation of the crankshaft.

Both the main bearings and the crank pins for the crankshaft must bemachined in order to form a bearing surface. Machining the main bearingsis straightforward since the crankshaft is merely rotatably driven aboutits axis and the main bearings machined by turning, grinding, or thelike.

Conversely, machining the crank pins to form the required bearingsurface presents a more difficult problem since the axis of the crankpins are radially offset from the rotational axis of the crankshaft.There have been a number of previously known devices and methods formachining the crank pins.

One previously known method for machining the crank pins is to rotatablydrive the crankshaft about the crank pins axis and then machine thecrank pins in any conventional fashion. This previously known method,however, is undesireable since the crankshaft must be rotatably drivenaround each different crank pin axis. As such, multiple sequentialmachining operations must be performed on the crankshaft which increasesthe overall machining costs and time for the crankshaft.

There have, however, been a number of previously known machines whichare designed to simultaneously machine all of the crank pins for thecrankshaft. These previously known machines typically comprise a firstmaster shaft having a plurality of offset crank pins which correspond tothe crank pins of the crankshaft which is to be machined. The mastershaft is rotatably mounted to a housing while another substantiallyidentical master shaft is rotatably mounted to one end of a cradle. Theother end of the cradle is pivotally mounted around the rotational axisof the first master shaft and movable between a first and a secondposition. Since the master shafts are substantially identical to eachother, each crank pin on the first master shaft has a correspondingcrank pin on the second master shaft which is both radially offset andangularly positioned the same.

A plate or girt is then rotatably mounted to each of corresponding crankpins on both master shafts so that, as the master shafts and thecrankshaft are rotatably driven in synchronism with each other, eachgirt replicates the cyclical movement for its associated crank pin onthe crankshaft. A tool bit mounted to each girt engages its associatedcrank pin on the crankshaft as the cradle is pivotted from its first andto its second position to thereby machine the crankshaft crank pins.Conventionally, the tool engages the crank pin diametrically as thecradle is pivoted from its first and to its second position.

One disadvantage of these previously known crankshaft machining devicesis that all crank pins are machined simultaneously with each other. Assuch, the tools as well as the crankshaft undergo a tremendous tool loador tool pressure during the machining operation. This high tool load notonly causes heating and occasional distortion of the crankshaft, butalso results in a relatively short tool life for the cutting tools. Assuch, the tools must be frequently replaced thereby resulting in downtime for the machine.

SUMMARY OF THE PRESENT INVENTION

The present invention provides a device for machining crank pins on acrankshaft which overcomes all the above-mentioned disadvantages of thepreviously known devices.

Like the previously known devices which simultaneously machine the crankpins, the device of the present invention comprises a master shafthaving crank pins corresponding to the crank pins of the crankshaft tobe machined rotatably mounted within a housing. A second master shaft isrotatably mounted to a cradle which, in turn, is pivotally mounted tothe housing about the rotational axis of the first master shaft.

Similarly, a plurality of girts are rotatably mounted between theircorresponding crank pins on the two master shafts for each crank pin tobe machined on the crankshaft. Consequently, these girts move in acyclical pattern corresonding to the cyclical movement of the crankshaftcrank pin as the master shafts and crankshaft are rotatably driven insynchronism with each other.

Unlike the previously known devices, however, a broach is secured toeach girt so that the broach moves tangentially with respect to itsassociated crank pin as the cradle is pivoted from its first and to itssecond position. The broaches thus machine the crank pins by turnbroaching.

BRIEF DESCRIPTION OF THE DRAWING

A better understanding of the present invention will be had uponreference to the following detailed description when read in conjunctionwith the accompanying drawing, wherein like reference characters referto like parts throughout the several views, and in which:

FIG. 1 is a fragmentary perspective view illustrating a preferredembodiment of the present invention;

FIG. 2 is a diagrammatic side view of the preferred embodiment of thepresent invention;

FIG. 3 is a side view taken substantially along line 3--3 in FIG. 5 andwith parts removed for clarity;

FIG. 4 is a view taken substantially along line 4--4 in FIG. 5 and withparts removed for clarity;

FIG. 5 is a front view of the preferred embodiment of the invention andwith parts removed for clarity;

FIG. 6 is a plan view taken substantially along arrow 6 in FIG. 4;

FIG. 7 is a view similar to FIG. 6 but illustrating a modificationthereof; and

FIG. 8 is a front diagrammatic view illustrating a crankshaft and onemaster shaft.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

With reference first to FIG. 8, a crankshaft 10 is thereshown indiagrammatic form which, in use, rotates about its axis 12. A pluralityof spaced main journals 14 are machined in any conventional fashion sothat they are coaxial with the crankshaft axis 12. In addition, apluraliy of crank pins 16 each have an axis parallel to, but radiallyoffset from, the crankshaft axis 12. The device of the present inventionmachines the crank pin 16 to form a bearing surface in a fashion to besubsequentially described in greater detail.

With reference then to FIGS. 1 and 2, the crankshaft machining device ofthe present invention comprises a housing 20 having a front 22, rear 30,bottom 28 and sides 24. A first master shaft 26 is rotatably mounted tothe housing 20 by any conventional means so that the first master shaft26 is adjacent to, but spaced upwardly from, the bottom 28 and inwardlyfrom the rear 30 of the housing 20. As best shown in FIG. 8, this mastershaft 26 is adapted to be rotatably driven about is axis 32 and includesa plurality of crank pins 34 which are radially offset from its axis 32of rotation. Furthermore, each crank pin 34 has an axis which is bothradially and angularly offset from the axis 32 by an amountcorresponding to the angular and radial offset of its correspondingcrank pin 16 of the crankshaft 10.

With reference then to FIGS. 2, 3 and 5, a cradle 40 includes two spacedside arms 42 which are pivotally mounted at one end 44 about the axis 32of the master shaft 26. A cross bar 48 extends between the arms 42adjacent their other end 50 so that the entire cradle 40 pivots in useabout the axis of the master shaft 26.

As best shown in FIGS. 3 and 5, a second master shaft 52, which issubstantially identical to the first master shaft 26, is rotatablymounted to the cradle side arms 42 adjacent their upper ends 50.Furthermore, the axis of the second master shaft 52 is parallel to andspaced from the axis of the first master shaft 26 despite the pivotalposition of the cradle 40.

As shown in FIGS. 1 and 2, a pair of crankshaft chucks 56 are rotatablymounted to the housing 20 so that the chucks 56 are coaxial with eachother and also parallel to the axes of the master shafts 26 and 52. Thechucks 56 are spaced apart from the other and are adapted to engageopposite ends of the crankshaft 10 to be machined. Any conventionalloading and unloading means 58 (FIG. 2) is employed to load and unloadthe crankshaft 10 into and out from the chucks 56. Furthermore, when thecrankshaft 10 is loaded into the chucks 56, the crankshaft is angularlypositioned so that each of its crank pins 16 is at the same angularposition as its corresponding crank pins on the master shafts 26 and 52.

With reference now to FIGS. 4 and 5, the present invention furthercomprises a plurality of substantially planar girts 60 so that one girt60 is associated with each crank pin 16 on the crank shaft 10 and, thus,the corresponding crank pins 34 on the master shafts 26 and 52. Eachgirt 60 is rotatably mounted adjacent its lower end 62 by conventionalbearings 61 to its associated crank pin 64 on the master shaft 26.Similarly, an upper end 66 of each girt 60 is rotatably mounted bybearings 63 to its associated crank pin 68 on the second master shaft52. The girt 60 includes a knuckle joint 71 adjacent its upperrotational connection with the crank pin 68 of the master shaft 52 toallow for small tolerances between the master shafts 26 and 52.

With reference now particularly to FIGS. 1 and 2, a motor 70 rotatablydrives a first gear 72 which is secured to the first master shaft 26.Idler gears 74 and 76 are in mesh with the gear 72 and respectivelyrotatably drive a pinion 78 secured to the second master shaft 52 and apinion 80 secured to one crank shaft chuck 56. A substantially identicalgearing arrangement is preferably provided on the opposite side 24 ofthe housing 20 so that, upon activation of the motor 70, the mastershaft 26 and 52 as well as the crankshaft chucks 56 are rotatably drivenin synchronism with each other.

With reference again to FIG. 4, the cyclical or circular movement of themaster shaft crank pins 34 impart a like cyclical or circular movementto the girts 60. Consequently, assuming that the cradle 40 is maintainedstationary, a forward end 90 of each girt 60 maintains a constant spacedapart relationship with respect to the crank shaft crank pin 16associated with that particular girt 60.

With reference now to FIGS. 3 and 4, as previously described, the cradle40 is pivotal between a first pivotal position, illustrated in phantomline, and a second pivotal position, illustrated in solid line. Althoughany conventional means can be used to pivot the girt between its firstand second pivotal positions, preferably a gear rack 92 (FIG. 3) mesheswith a motor driven pinion 94 rotatably mounted to the housing 20 sothat rotation of the pinion 94 swings the cradle forwardly between itsfirst and second pivotal positions. Preferably, a servomotor and encoder95 are used to drive the pinion 94.

With reference now to FIGS. 4 and 6, a broach 96 is secured to theforward end 90 of each girt 60. Each broach 96 includes a plurality ofcutting blades 98 which protrude progressively more outwardly from thetop of the broach and towards its bottom as best shown in exaggerationin FIG. 4. Consequently, as the broach moves from its pivotal position(phantom line) and to its second pivotal position, the broach cuttingblades 98 tangentially engage the crankshaft crank pin 16 and performprogressively deeper cuts with the lowermost cutting blade 98' machiningthe crankshaft crank pin 16 to its final desired diameter.

With reference now to FIG. 6, in one form of the invention, the cuttingblades 98 on the broaches 96 extend generally parallel to the axis ofthe crank pin 16. Thus, as the cutting blades 98 engage the crankshaftcrank pin 16, they shave the crank pin 16 thus machining by turnbroaching. In addition, preferably the cutting blades 98 on one broach96 are offset from the cutting blades 98 on the broach 96' on adifferent girt 60 thereby minimizing the number of cutting blades 98which engage the crank pins 16 during any pivotal position of the girt60. Consequently, by offsetting the cutting blades 98 on one broach fromthe other broaches 96', the tool pressure is minimized during the turnbroaching operation.

With reference now to FIG. 7, an alternate form of the broach 96 isthereshown in which the cutting blades 98" are skewed with respect tothe axis of the crankshaft crank pin 16. Thus, when the broach 96illustrated in FIG. 7 is substituted for the broach illustrated in FIG.6, the crank pins 16 are machined by skiving rather than by shaving.Both shaving and skiving, however, when applied to a rotating work as inthe instant invention are collectively known as turn broaching.

In operation, the crankshaft is loaded into the crankshaft chucks 56 sothat the crankshaft crank pins 16 are angularly at the same position astheir corresponding or associated crank pins 34 on the master shafts 26and 52. At this time, the cradle 40 is in its lowermost position so thatthe girts 60 are also in their lower or first position illustrated inphantom line in FIG. 4.

The motor 70 then rotatably drives the master shafts 26 and 52 andcrankshaft 16 in synchronism with each other. Simultaneously, the pinion94 (FIG. 3) is rotatably driven thus pivoting the cradle 40 from itsfirst position, illustrated in phantom line of FIG. 4 and to its secondposition, illustrated in solid line in FIG. 4. In doing so, each broach96 tangentially engages its associated crankshaft crank pin 16 tothereby machine the crankshaft crank pin 16. Furthermore, since in thepreferred embodiment of the invention the broach blades on one girt 60are longitudinally offset from the broach blades on the other girts,tool pressure is minimized during the turn broaching operation.

When the cradle 40 reaches its second pivotal position, the turnbroaching operation on the crank pin 16 is completed and the crankshaft10 is removed and replaced with a new crankshaft 10 whereupon the aboveprocess is repeated.

From the foregoing, it can be seen that the present invention provides adevice for turn broaching the crank pins of a crankshaft. Since only arelatively small amount of material is removed from the crank pins byeach broach cutting blade 98, tool pressure on the crankshaft crank pinsis minimized. This in turn, minimizes heating and possible thermaldistortion of the crankshaft during the machining process also lengthensthe tool life for the broaches 96.

The servomotor and encoder 95 also enables the machine to be used withconventional plunge turning, facing tools and the like.

Having described my invention, many modifications thereto will becomeapparent to those skilled in the art to which it pertains withoutdeviation from the spirit of the invention as defined by the scope ofthe appended claims.

I claim:
 1. A device for machining the crank pins of a crankshaft comprising:a housing, a pair of substantially identical master shafts, each master shaft having one crank pin associated with each other and with each crank pin on the crankshaft, means for rotatably mounting one master shaft to the housing, means for rotatably mounting the crankshaft to the housing, a cradle, means for pivotally mounting said cradle to said housing about an axis of said one master shaft between a first and a second pivotal position, means for rotatably mounting the other master shaft to said cradle so that said master shafts are spaced apart and parallel to each other, a plurality of generally planar girts, means for rotatably mounting one girt to the associated crank pins on said master shafts, means for rotatably driving said master shafts and the crankshaft in synchronism with each other, a plurality of broaches, one broach being mounted to each girt adjacent its associated crankshaft crank pin and at a position so that said broaches move tangentially with respect to their associated crankshaft crank pins as said cradle moves between said first and said second pivotal positions, and means for moving said cradle between said first pivotal position and said second pivotal position so that said broaches engage and machine the crank pins on the crankshaft.
 2. The invention as defined in claim 1 wherein each said broach comprises a plurality of spaced cutting blades which sequentially engage its associated crankshaft crank pin as said cradle moves from said first and to said second position.
 3. The invention as defined in claim 2 wherein the cutting blades on one broach are tangentially offset with respect to the pivotal axis of said cradle from the cutting blades on another broach.
 4. The invention as defined in claim 2 wherein said cutting blades are skiving cutting blades.
 5. The invention as defined in claim 2 wherein said cutting blades are shaving cutting blades.
 6. The invention as defined in claim 1 wherein said moving means comprisesa gear segment secured to said cradle, a pinion rotatably mounted to said housing and in mesh with said gear segment, and means for rotatably driving said pinion.
 7. The invention as defined in claim 6 wherein said means for rotatably driving said pinion comprises a servomotor and encoder. 